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Critical drawback of poor stiffness in traditional auxetic materials limits them to be applied where negative Poisson’s ratio behavior and excellent load-bearing capacity are simultaneously desired. In this work, a general prescription for designing auxetic lattice structures with high stiffness and controllable isotropic/anisotropic elastic properties is proposed. Based on it, we rationally design a class of novel auxetic lattice structures whose deformation is mainly governed by the stretching mechanisms and conducted an investigation on a tree-like re-entrant structure. A combination of theoretical predictions, numerical simulations and tensile test experiments have been carried out to gain a comprehensive understanding of the structural in-plane elastic mechanical properties along both the principal axes as well as in the off-axis directions. Besides, theoretical model for designing tree-like re-entrant structure with isotropic elastic properties is established and experimentally verified with specimens fabricated with CFRP composite. The results of this research has proven the tree-like re-entrant structure exhibits excellent effective Young’s modulus, shear modulus and obvious negative Poisson’s ratio effect along omni-direction. Investigation on the directional dependence of structural effective elastic properties has further indicated the proposed structure presents a great potential for designing auxetic material with controllable anisotropic elastic properties. In particular, the proposed structure is capable in achieving isotropic design with any negative Poisson’s ratio between −1 and 0. The design philosophy presented in this paper provides a general prescription for solving the challenge of poor stiffness in traditional auxetic materials and paves a new way for isotropic auxetic design.

Sandwich core materials that offer superior mechanical properties at minimum weight are essential in designing high-performance sandwich structures. Hierarchical materials are ideal templates for this purpose. In this paper, we investigate the mechanical performance of a pyramidal–pyramidal hierarchical lattice material to highlight its potential as the core material for sandwich structures. Three-dimensional failure mechanism maps for the pyramidal–pyramidal hierarchical lattice material are developed under different loading conditions and the results are compared to finite element simulations. Next, we study the mechanical response and failure modes of a sandwich panel with self-similar pyramidal lattice core construction subjected to in-plane compression and three-point bending. The current study indicates that the pyramidal–pyramidal hierarchical configuration can improve the load bearing capacity and core buckling resistance of the sandwich structures at low density. The study provides insights into the role of structural hierarchy in tuning the mechanical response of the lattice materials and expands the application envelope of lightweight sandwich structures by effectively increasing the structural buckling resistance.

Recycling of drinking water treatment residuals (DWTRs) in aquatic environment remediation can provide numerous benefits. The hazardous effect of DWTR metals on the environment is shown to be limited; however, DWTR may release excessive nitrogen and organic matter, hindering recycling in the aquatic environment. To eliminate any potential unfavorable effect, self-purification via intermittent aeration incubation for DWTRs was developed. Results indicated that after approximately 5–6 months of incubation, the easily released nitrogen and organic matter in the DWTRs were mostly removed. The removed nitrogen was found to mainly consist of ammonium nitrogen from inorganic and organic nitrogen groups in the DWTRs. The removed organic matter consisted mainly of humic-like substances associated with the carboxyl group, distributed on the surface of the DWTRs. Biological mechanisms for effective nitrogen and organic matter removal were further explored based on the analysis of bacterial community structure, which indicated that the dominant bacteria genera (e.g., Geothrix, Methylotenera, and Geobacter) in the DWTRs after incubation were closely related to nitrogen and carbon cycles. In addition, the phosphorus adsorption of the DWTRs after incubation was maintained, and the specific surface area, total pore volume, microporosity, and mesoporosity of the DWTRs after incubation tended to increase because of organic matter removal. Accordingly, intermittent aeration not only addressed the concerns caused by potential excessive release of nutrients from DWTRs but also enhanced the favorable effect of DWTRs on biogeochemical cycles. Self-purification can potentially promote the beneficial recycling of DWTRs in the aquatic environment.

The weakest link in traditional sandwich beams constructed of carbon fiber reinforced polymer (CFRP) honeycomb core is arguably the bonded face sheet-core interface. This has limited the development and the expanded application of these sandwich structures. To overcome this, in this paper, a type of interface-reinforced honeycomb core is proposed to improve the bonding by enlarging the bonding area and thus increasing the strength of the face sheet-to-core attachment. A modified tailor-folding method is employed to fabricate two designs of the interface-reinforced honeycomb. The two interfaces reinforced cores are identical, except for the presence of machined holes in the strengthened fillet created to accommodate adhesive fillets formed during bonding. Double cantilever beam (DCB) test is performed to compare the bonding and behavior of the beams, which are tested alongside beams of a traditional honeycomb that is used as a control sample. In addition, the influences of cell wall thickness and loading direction with respect to the orientation of core macrostructures are also investigated. Modified Beam Theory (MBT) and Elastic Foundation Model (EFM) are employed to calculate the critical strain energy release rate. Overall, the interfaced-reinforced cores performed much better than the traditional core, with the former and latter being stronger in the transverse and longitudinal directions, respectively. The various failure modes observed from the test are analyzed and used to illustrate the strengthening mechanics operating in the interface-reinforced honeycomb.

In this paper, three-dimensional failure mechanism maps are developed to investigate the in-plane compressive characteristics of all-composite honeycomb sandwich columns and optimize their load-weight efficiency. Analytical models are derived based on five possible failure modes, including shear macro-buckling, intracellular dimpling, face wrinkling, face fracture and debonding. The dominant failure mode can be determined by three dimensionless geometrical parameters, i.e., the length-height ratio of the sandwich column, the height ratio of face and core, and the relative density of honeycomb core. A series of three-dimensional failure mechanism maps are constructed based on the fiber orientations in the face sheet and honeycomb core. It is observed that failure mode transforms with dimensionless geometrical parameters in a spatial region. A typical three-dimensional failure mechanism map is experimentally validated. Sectional views in different directions are used to locate the boundaries of failure modes. All-composite honeycomb sandwich columns are designed and fabricated using the tailor-folding method. In-plane compressive experiments are carried out to verify the analytical models and three-dimensional failure mechanism map. The experimental results agree well with analytical predictions. Optimal geometrical design is performed to obtain the geometrical relations of honeycomb sandwich columns with the highest load-weight efficiency under in-plane compression. The novelty of this work lies in broadening the failure mechanism map to spatial region and optimal geometrical design.

This paper introduces a new methodology for generating three-dimensional (3D) negative Poisson’s ratio behavior with lattice representations of the rotating rigid mechanism as a starting point. Based on it, a class of new 3D auxetic lattice structures is proposed. The elastic properties of a representative 3D auxetic lattice structure, including the homogenized Young’s modulus and Poisson’s ratio along the three principal axes, are systematically investigated in a combination of analytical predictions, numerical simulations and experimental tests. Moreover, effects of the structural geometrical parameters and specimen size on the elastic properties as well as structural nonlinear mechanical responses along the principal axes are carefully discussed. Different from most traditional 3D auxetic materials that are only capable of achieving negative or positive Poisson's ratio, our results suggest that the homogenized Poisson’s ratio effect of the proposed 3D lattice structure along all principal axes can be tuned from positive to negative in a wide range. The excellent design flexibility would help to expand and hasten the adoption of the new 3D auxetic lattice structures in engineering applications.

Mechanical properties and failure mechanisms of sandwich panels with “corrugated-pyramidal” hierarchical lattice cores were investigated through analytical modeling and detailed numerical simulations. This included studying the behavior of hierarchical lattice core material under compression and shearing, as well as investigating the mechanical performance of sandwich panels subjected to in-plane compression and three-point bending. Failure maps were constructed for the hierarchical lattice cores, as well as sandwich panels with hierarchical lattice cores by deriving analytical closed-form expressions for strength for all possible failure modes under each loading. 3D printed samples were manufactured and tested under out-of-plane compression in order to provide limited experimental validation of the study. Our study provides insights into the role of structural hierarchy in tuning the mechanical behavior of sandwich structures, and new opportunities for designing ultra-lightweight lattice cores with optimal performance.

The bending characteristics of all-composite honeycomb sandwich beams were investigated by a three-dimensional failure mechanism map and verified by three-point bending tests. In this paper, analytical models were used to predict the three-point bending stiffness, failure load and failure modes of all-composite hexagon honeycomb sandwich beams. A three-dimensional failure mechanism map was generated to characterize the dominant failure mechanism based upon failure load criteria for shear buckling, shear fracture, debonding, intracellular dimpling and face fracture. The tailor-folding method was used to fabricate the all-composite honeycomb sandwich beams. To verify the analytical models and three-dimensional failure mechanism map, three-point bending tests were carried out on the sandwich beams with different core relative densities, face thicknesses and loading spans. It was observed that the analytical predictions were in good agreement with the experimental results. A single case with the supreme load-weight ratio on the failure mechanism map has been identified and verified. Besides, the paths of maximum load design for a series of geometrical parameters were also traced. The study provides insights into the role of the physical dimension in tuning the flexural property of the sandwich structure and expands the application envelope of the failure mechanism map by effectively increasing the structural analytical dimensionality.

In this paper, considering a supply chain subject to stochastic demand, we present a newsvendor model to study the game process between a supplier owning private cost information and a retailer suffering from inventory inaccuracy problem. We present that by setting the contract parameters appropriately, both partners have the right incentive for maximizing the total supply chain profit: the supplier share information actively by choosing the contract designed for his marginal production cost, while the retailer׳s rational decision concurs with the overall optimal decision. We further study the supply chain performance and the interval of the coordinating contract parameters under different situations by illustrating the model through some numerical assumptions, establishing and highlighting the conditions under which the RFID technology is preferable to the system.